In a medical image diagnosis apparatus such as an X-ray CT (computed tomography) apparatus or an X-ray apparatus, a high-power power device (semiconductor device directed at electric power unit) is included in a converter and an inverter of an X-ray high voltage apparatus in order to generate a high voltage to be supplied to an X-ray tube. When the medical image diagnosis apparatus is operating, the power devices of the X-ray high voltage apparatus undergo a rapid increase in temperature each time that X-rays are generated.
The output power of the X-ray high voltage apparatus is a large amount of several tens of kilowatts to hundreds of kilowatts. Consequently, an IGBT (insulated gate bipolar transistor) module or an MOSFET (metal-oxide-semiconductor field-effect transistor) module or the like is often used as a power device of a converter and an inverter in the X-ray high voltage apparatus.
As a conventional X-ray high voltage apparatus, an apparatus is known in which a converter is formed so as to realize a stable power factor even if an input AC power supply voltage fluctuates.
However, according to the conventional technology, in a medical image diagnosis apparatus such as an X-ray CT apparatus or an X-ray apparatus, the accumulation of damage to a power device provided in a converter or an inverter of an X-ray high voltage apparatus or to a bonding wire joined thereto is one of the main causes of a failure of the X-ray high voltage apparatus. Consequently, there is a problem that if such a failure suddenly occurs during a radiography operation, image data based on the radiography operation is wasted and it is necessary to re-perform the radiography operation.
It is known that damage to a power device is due to strain caused by expansion and contraction of an internal component member that is caused by temperature amplitudes. However, in the case of a medical image diagnosis apparatus, the number of CT scans and the number of X-ray radiographs vary depending on the conditions of use such as the diagnostic purpose and the physique of the patient, and temperature amplitudes of the power devices or bonding wires vary significantly. Hence, a heat cycle life or a power cycle life of a power device cannot be determined based on a constant temperature amplitude, and heretofore it has been difficult to assess the degree of damage to a power device or to predict the amount of damage thereto.